1. Field of the Invention
This invention relates to improving the light fastness of organic substrate materials and, more particularly, to improving the light fastness of organic compounds useful as dyestuffs. The present invention is particularly directed to improving the light fastness of organic substrate materials occurring in photographic materials, e.g., color films, prints, etc.; in colored polymers useful as agricultural vinyl cover sheets, umbrellas, tents, etc.; of fluorescent whitening agents; and dyed textiles, etc.
2. Discussion of the Prior Art
It is commonly accepted that organic substances such as organic dyes tend to fade by the action of light. Extensive studies have been carried out in various technical fields including those for printing ink, textile dyeing as well as color photography, in an effort to improve the light fastness of organic dyes. The present invention is advantageously used to improve the light fastness of these organic substances.
In the following description of the invention, the term "organic substrate material" or "organic substrate" refers to materials appearing colored or colorless to human eye under the illumination of sunlight, as well as those having absorption peaks which lie in the infrared or in the ultraviolet region as in the case of optical whitening agents. In other words, the organic substrate materials of the present invention are organic materials (colorants and dyes) having their absorption peaks in the wavelength range of from 300 to 800 nm.
In the present specification, the term "dye" or "dyestuff" refers to an organic material which appears colored to the human eye under the illumination of sunlight. The term "light" conceptually involves electromagnetic radiation with wavelengths up to about 800 nm and, thus, includes ultraviolet rays below 400 nm, visible light of from about 400 nm to about 700 nm and infrared rays of from about 700 to about 800 nm.
It is widely known that organic substrate materials such as, for example, dyes and coloring agents, tend to fade under the influence of light irradiation. A number of technical reports dealing with methods of suppressing such tendency or of improving the light fastness of such materials are known. For example, U.S. Pat. No. 3,432,300 discloses that the light fastness of organic compounds such as indophenol, indoaniline, azo and azomethine dyes to visible and UV light is improved by the use of certain phenol derivatives containing a condensed heterocyclic structure. The Theory of the Photographic Process, authored by Mees et al, 3rd Ed. (1967) teaches in Chapter 17 that silver halide color photographic products generally give rise to azomethine or indoaniline dyes formed upon the reaction of the oxidation product of an aromatic primary amine developing agent and a color coupler. Also, various patents teach means to improve the stability to light of the color photographic images. Compounds which effectively improve the light fastness of the co-existing dye include, for example, the hydroquinone derivatives set forth in U.S. Pat. Nos. 2,360,290, 2,418,613, 2,675,314, 2,701,197, 2,704,713, 2,728,659, 2,732,300, 2,735,765, 2,710,801 and 2,816,028 and British Pat. No. 1,363,921, etc.; the gallic acid derivatives set forth in U.S. Pat. Nos. 3,457,079 and 3,069,262, Japanese Patent Publication No. 13496/1968, etc.; the p-alkoxyphenols set forth in U.S. Pat. Nos. 2,735,765 and 3,698,909; and the chroman and coumarane derivatives set forth in U.S. Pat. Nos. 3,432,300, 3,574,626, 3,574,627, 3,698,909, 3,573,050, 3,764,327 and 4,015,990, etc. These compounds are effective to prevent the fading or the discoloration of dye images by light to a certain but unsatisfactory extent.
British Pat. No. 1,451,000 discloses that the stability of organic substrate materials to light is enahnced by the use of azomethine quenching compounds which have their absorption peaks at a longer wavelength than the substrate material; unfortunately, the azomethine quenching compound is itself colored and adversely affects the color hue of the substrate material. Metal chelates can be used to prevent the degradation of polymeric substances caused by light as described in the following literature: J. P. Guillory and R. S. Becker, J. Polym. Sci., Polym. Chem. Ed., 12, 993 (1974), and R. P. R. Ranaweera and G. Scott, J. Polym. Sci., Polym. Lett. Ed., 13, 71 (1975), etc. Stabilization of dyes against light by the use of metal chelate is also discussed in U.S. Patent 4,050,938, Japanese Patent Application (OPI) No. 87649/1975 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application") and Research Disclosure 15162 (1976). However, the disclosed metal chelates exhibit an unsatisfactory fade preventing effect and when the metal chelates are employed in a photographic emulsion for practical use, the disclosed metal chelates desensitize the silver halide probably due to an undesirable interaction with silver. Also, the metal chelates exhibit an undesirably poor solubility in common organic solvents. The latter drawback limits the working concentration of the chelate in the system and, thus, leads to an insufficient fade prevention. Moreover, these chelates cannot be present in a high concentration since they themselves are comparatively deeply colored, and adversely affect the color hue and the color purity of the dyes they are supposed to protect.
Furthermore, good fade preventing or light fastness improving agents for cyan dyes have not been known. While cyan dye images per se are generally color fast enough not to require any color fade preventing agent, using the present invention, cyan couplers or dyes having elaborate and highly developed structures would not be needed and inexpensive cyan dyes and couplers could be used, which is practically advantageous.